Peterson : Miocene Beds of Nebraska and Wyoming. 51 



Transverse diameter of Mj 36 



Anteroposterior diameter of M-j 49 



Transverse diameter of M T 37 



Amphicyon superbus, sp. nov. 



(Type Specimen No. 1589, Cam. Mus. Cat. Vert. Foss.) 



(Plate XVIII.) 



This species is represented by an exceptionally well preserved skull 

 with the lower jaws, and portions of the skeleton. Only the skull and 

 lower jaws are freed from the matrix and are illustrated in connection 

 with this description. The specimen was found near the Agate 

 Spring Fossil Quarry and in the same horizon. The type, 17 No. 

 1589, is remarkable for its close resemblance to Cams; in fact were 

 it not for the relatively smaller brain case and the presence of M-& it 

 might well be taken for a member of that genus. 



The principal cranial characters of the type are as follows : 

 The skull is mesencephalic, and the brain case is small. If, Cj, 

 P|, Mf . On comparing it with Cants occidental the following dif- 

 ferences are noticeable. The fossil represents an animal very nearly 

 the size of a fully adult gray wolf, but the skull is shorter and broader, 

 the occipital condyles smaller, the basioccipital and basisphenoid of 

 greater transverse diameter, the paroccipital processes further separated 

 from the tympanic bulla, the mastoid larger, the tympanic bulla smaller, 

 and the postglenoid process heavier. The most important differences 

 from that of Cams occidentalis are perhaps the relatively smaller brain 

 case, the presence of M^, the smaller sectorial tooth, with the larger 

 internal tubercle, the larger M-, and the shorter and broader skull. 

 In size and position all the foramina are nearly identical with those in 

 Cam's occidentalis. 



The mandible, excepting the larger and deeper temporal fossa, is 

 very similar to that of the wolf. 



On comparing the type with that of Amphicyon americanus Wort- 

 man {American Journal of Science, Vol. XL, pp. 200-204, 1901) it 

 is seen that the skull is smaller, the canines smaller and more rounded, 

 the premolars larger, and the second and third premolars smaller. 

 The internal cusp on the fourth upper premolar of Amphicyon superbus 

 has a greater development, M^ has a more internal position in the 

 alveolar border than in Amphicyon americanus. 

 17 Two individuals of the same species were found together. 



